ABCG2 and cancer: First, we selected 21 cancer stemness-related genes, OPN, OCT4, NANOG, SOX2, HIF1α, BMI1, ABCG2, CK19, NOTCH1, KLF4, CD44, CD90, CD133, CD117, CD24, EPCAM, TCF3, TCL, CTNNB1, HEY1, and C-MYC.